Extra gate device for nanosheet

ABSTRACT

A method for forming semiconductor devices includes forming a highly doped region. A stack of alternating layers is formed on the substrate. The stack is patterned to form nanosheet structures. A dummy gate structure is formed over and between the nanosheet structures. An interlevel dielectric layer is formed. The dummy gate structures are removed. SG regions are blocked, and top sheets are removed from the nanosheet structures along the dummy gate trench. A bottommost sheet is released and forms a channel for a field effect transistor device by etching away the highly doped region under the nanosheet structure and layers in contact with the bottommost sheet. A gate structure is formed in and over the dummy gate trench wherein the bottommost sheet forms a device channel for the EG device.

BACKGROUND

Technical Field

The present invention relates to extra gate (EG) device integration intonanosheet fin complementary metal oxide semiconductor (CMOS) devices,and more particularly to devices and methods for making the same.

Description of the Related Art

In nanometer scale devices, gate structures are often disposed betweenfin structures or other conducting structures, such as nanosheets. Inmany instances, the conducting or semiconducting structures are formedcloser together due to scaling to smaller node technology sizes. Thiscan be a limiting factor in the reduction of the device size scaling.

While finFETs and/or nanosheets can benefit from tight device-devicespacing, these dimensions may limit scaling of these devices. Further,devices requiring thicker dielectric for higher voltage operation areeven more severely limited in the allowable dimensions. Higher voltagedevices for input/output circuits require thicker gate dielectrics ascompared to standard gate devices, which have a lower voltage and may beemployed, e.g., in logic devices. However, spacing between sheets needsto be small to realize capacitance benefits.

The increased gate dielectric thickness needed for high voltage devicesis thicker than the optimal space between sheets. Thus, there is a needfor a new device structure and method to build the structure to enablethe integration of high voltage or extra gate devices with standardnanosheet devices.

SUMMARY

A method for forming semiconductor devices includes doping a surface ofa substrate in exposed areas where extra gate (EG) devices are to beformed to form a highly doped region and forming a stack of alternatinglayers on the substrate over single gate (SG) regions and the EGregions. The stack is patterned to form nanosheet structures. A dummygate structure is formed over and between the nanosheet structures. Aninterlevel dielectric layer is formed over the dummy gate structure andthe nanosheet structures, and dummy gate structures are removed to forma dummy gate trench. The SG regions are blocked. Top sheets are removedfrom the nanosheet structures along the dummy gate trench. At least onebottommost sheet including a semiconductor layer is released to form achannel for a field effect transistor device by etching away the highlydoped region under the nanosheet structure and layers in contact withthe at least one bottom most sheet. A gate structure is formed in andover the dummy gate trench wherein the at least one bottommost sheetforms a device channel for the EG device.

In another method, a stack of alternating layers is formed on asubstrate over single gate (SG) regions and extra gate (EG) regions. Ahard mask is formed over the stack. The hard mask and the stack arepatterned to form nanosheet structures. A dummy gate material is formedover the hard mask and over sides of the nanosheet structures in SG andEG regions. The dummy gate material is planarized and forms dummy gatestructures by patterning the dummy gate over the SG and EG nanosheets. Aspacer is formed around the dummy gate structure by depositing aconformal dielectric material and using a directional etching process toremove dielectric material from horizontal surfaces and leave dielectricmaterial on vertical surfaces. Source and drain regions for NFETs andPFETs are formed.

In another embodiment, a method for forming semiconductor devicesincludes forming a stack of alternating layers on a substrate oversingle gate (SG) regions and extra gate (EG) regions; forming a hardmask over the stack; patterning the hard mask and the stack to formnanosheet structures; forming a dielectric material over the hard maskand over sides of the nanosheet structures in EG regions; recessing thedielectric material below a topmost semiconductor layer of the nanosheetstructures in EG regions; forming a spacer layer over side portions ofthe topmost semiconductor layer to protect the topmost semiconductorlayer in EG regions; removing the dielectric material; etching awaysemiconductor layers of the nanosheet structures for EG devices; etchingaway layers of the nanosheet structures for the EG devices; and forminga gate structure in and over a dummy gate trench wherein the topmostsheet forms a device channel for the EG device.

A dielectric material (e.g., interlevel dielectric (ILD)) is depositedand planarized to be coplanar with the dummy gate structures. The dummygate material is removed, and SG device regions are blocked. Thenanosheet structures are removed down to a bottom sheet in the EGregions. Blocking material is removed from the SG regions, and thesacrificial layers are removed. N-type materials from the bottomportions of the EG regions and the sacrificial materials in the SGregions are removed. A thick dielectric is formed on channels of thenanosheets for the SG and EG regions and then the EG regions areblocked. The thick dielectric in the SG regions is removed and a thindielectric is formed in the SG regions. The blocking materials areremoved from the EG regions. A high k gate dielectric is deposited overthe SG and EG regions and forms the remaining portions of the gate stackelectrodes in the SG and EG regions.

A semiconductor device includes a substrate and nanosheet structures.The nanosheet structures each includes a stack of alternating layers onthe substrate over single gate (SG) regions and extra gate (EG) regions.The nanosheet structures each includes a central gate structure regionand source and drain regions on end portions of the nanosheetstructures. The central gate structure region includes a singlesemiconductor layer of the stack extending between the source and drainregions for EG devices to enable a thicker gate dielectric for the EGdevices.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 is a cross-sectional view of a substrate having a P well formedtherein in accordance with the present principles;

FIG. 2 is a cross-sectional view of the substrate of FIG. 1 having an Nwell formed therein in accordance with the present principles;

FIG. 3 is a cross-sectional view of the substrate of FIG. 2 havingsingle gate (SG) regions blocked to form highly doped regions in extragate (EG) regions in accordance with the present principles;

FIG. 4 is a cross-sectional view of the substrate of FIG. 3 havingalternating layers of Si and SiGe formed thereon to be removed to at alater point in the process flow to form or release the nanosheet channelregions;

FIG. 5 is a cross-sectional view of the substrate of FIG. 4 having dummygates, spacers and source and drain regions formed over and in betweennanosheet structures in accordance with the present principles;

FIG. 6 is a cross-sectional view of the substrate of FIG. 5 having thedummy gates pulled from over and in between nanosheet structures inaccordance with the present principles;

FIG. 7 is a cross-sectional view of the substrate of FIG. 6 having SGregions blocked to remove sheets along a dummy gate trench line for EGdevices in accordance with the present principles;

FIG. 8 is a cross-sectional view of the substrate of FIG. 7 having abottommost sheet released and the highly doped region removed to form abottom release region for EG devices and sacrificial sheets removed forSG devices in accordance with the present principles;

FIG. 9 is a perspective view of the device of FIG. 8 with materialsremoved to view the bottommost layer, showing a gate structure formedand showing source and drain regions formed in accordance with thepresent principles;

FIG. 10 is a cross-sectional view of a nanosheet structure after a dummygate pull and having trenches formed on sides of the structure inaccordance with another embodiment;

FIG. 11 is a cross-sectional view of the substrate of FIG. 10 having thetrenches filled with a dielectric material and recessed below a topmostsheet in accordance with the present principles;

FIG. 12 is a cross-sectional view of the substrate of FIG. 11 havingspacers formed to protect the topmost sheet in accordance with thepresent principles;

FIG. 13 is a cross-sectional view of the substrate of FIG. 12 having theporous material removed in accordance with the present principles;

FIG. 14 is a cross-sectional view of the substrate of FIG. 13 havingdielectric (oxide) layers removed from the nanosheet structure for EGdevices in accordance with the present principles;

FIG. 15 is a cross-sectional view of the substrate of FIG. 14 havingsemiconductor layers other than the topmost layer removed from thenanosheet structure for EG devices in accordance with the presentprinciples;

FIG. 16 is a cross-sectional view of the substrate of FIG. 8 having afirst dielectric layer formed on EG devices and SG devices in accordancewith the present principles;

FIG. 17 is a cross-sectional view of the substrate of FIG. 16 having thefirst dielectric layer removed from the SG devices and an oxide formedon the SG devices by blocking the EG devices in accordance with thepresent principles;

FIG. 18 is a cross-sectional view of the substrate of FIG. 17 having ahigh-k dielectric layer formed on EG devices and SG devices inaccordance with the present principles;

FIG. 19 is a cross-sectional view showing a gate structure in greaterdetail in accordance with the present principles; and

FIG. 20 is a block/flow diagram showing methods form formingsemiconductor devices with different gate dielectric sizes in accordancewith illustrative embodiments.

DETAILED DESCRIPTION

In accordance with the present principles, extra gate (EG) devices andsingle gate (SG) devices are integrated together in a complementarymetal oxide semiconductor (CMOS) device. EG devices work with highervoltages and therefore include thicker gate dielectric layers on gatestructures. When nanosheets are employed, the nanosheets are finelylayered for single gate (SG) structures. SG structures refer to deviceswith thinner gate dielectric. SG devices may be employed, e.g., in logicdevices. To mix EG and SG devices is difficult since the EG device needa thicker dielectric than the SG devices. For example, EG devices need agate dielectric of about 3-5 nm while SG devices need about 1-2 nm. Thepresent principles provide methods and devices that integrate the EG andSG devices on a same chip (e.g. CMOS chip). Spacing between sheets needsto be small enough to realize capacitance benefits (e.g., similar to finpitch scaling for fin field effect transistors (finFETs). Optimal sheetspacing may be about 8 nm. This space is not enough for appropriate EGdielectric and gate electrode fill EG device structures are provided,which can be co-integrated with a nanosheet. The EG (high voltage)devices can be co-integrated with nanosheet SG (low voltage) devices,where EG devices include a larger space for the EG dielectric film andmetal gate formation. Further, the present principles provide blockmasking to process EG devices and SG devices in a same processingsequence on a same chip to form different gate dielectric layers foreach device type.

It is to be understood that the present invention will be described interms of a given illustrative architecture; however, otherarchitectures, structures, substrate materials and process features andsteps may be varied within the scope of the present invention.

It will also be understood that when an element such as a layer, regionor substrate is referred to as being “on” or “over” another element, itcan be directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

The present embodiments may include a design for an integrated circuitchip, which may be created in a graphical computer programming language,and stored in a computer storage medium (such as a disk, tape, physicalhard drive, or virtual hard drive such as in a storage access network).If the designer does not fabricate chips or the photolithographic masksused to fabricate chips, the designer may transmit the resulting designby physical means (e.g., by providing a copy of the storage mediumstoring the design) or electronically (e.g., through the Internet) tosuch entities, directly or indirectly. The stored design is thenconverted into the appropriate format (e.g., GDSII) for the fabricationof photolithographic masks, which typically include multiple copies ofthe chip design in question that are to be formed on a wafer. Thephotolithographic masks are utilized to define areas of the wafer(and/or the layers thereon) to be etched or otherwise processed.

Methods as described herein may be used in the fabrication of integratedcircuit chips. The resulting integrated circuit chips can be distributedby the fabricator in raw wafer form (that is, as a single wafer that hasmultiple unpackaged chips), as a bare die, or in a packaged form. In thelatter case the chip is mounted in a single chip package (such as aplastic carrier, with leads that are affixed to a motherboard or otherhigher level carrier) or in a multichip package (such as a ceramiccarrier that has either or both surface interconnections or buriedinterconnections). In any case the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of either (a) an intermediate product, such as a motherboard, or(b) an end product. The end product can be any product that includesintegrated circuit chips, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

It should also be understood that material compounds will be describedin terms of listed elements, e.g., SiGe. These compounds includedifferent proportions of the elements within the compound, e.g., SiGeincludes Si_(x)Ge_(1-x) where x is less than or equal to 1, etc. Inaddition, other elements may be included in the compound and stillfunction in accordance with the present principles. The compounds withadditional elements will be referred to herein as alloys.

Reference in the specification to “one embodiment” or “an embodiment” ofthe present principles, as well as other variations thereof, means thata particular feature, structure, characteristic, and so forth describedin connection with the embodiment is included in at least one embodimentof the present principles. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment”, as well any other variations,appearing in various places throughout the specification are notnecessarily all referring to the same embodiment.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This may be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIG. 1, a partially fabricateddevice 10 is depicted in accordance with the present principles. Thedevice 10 includes substrate 12. The substrate 12 may include anysuitable semiconductor materials, e.g., Si, SiGe, SiC, III-V materials,(e.g., GaAs, InP, etc.) or any other suitable substrate material. In oneembodiment, the substrate 12 may be processed for complementary metaloxide semiconductor (CMOS) fabrication, which includes p-type devicesand n-type devices. The devices may include field effect transistors(FETs). In one embodiment, the FETs may include FETs formed usingnanosheets. Nanosheets include a plurality of thin layers processedtogether to form fin structures or other structures. In the embodimentsdescribed herein, the device 10 will integrate SG and EG devices in asame processing sequence and use the same nanosheet structure for bothdevice types.

A block level lithography process may include forming a resist or othermasking materials 18 on the substrate 12 and patterning the mask 18 tocover a p-type field effect transistor (PFET) region 16 and expose ann-type field effect transistor (NFET) region 14. The NFET region 14 isthen implanted with P type dopants to form a PFET well 22 (FIG. 2). Itshould be understood that the order of well formation may be reversed,e.g., the block mask 18 may be patterned to cover the n-doped region todope the p-doped wells first and the process steps of FIGS. 1 and 2 canbe reversed.

Referring to FIG. 2, a block level lithography process may includeforming a resist or other masking materials 24 on the substrate 12 andpatterning the mask 24 to cover the P well 22 and expose the PFET region16. The PFET region 16 is then implanted with N type dopants to form anN well 26.

Referring to FIG. 3, the block level lithographic mask 24 is replaced byanother lithographic mask 34. The masks 18, 24, 34 may include a resistor a hard mask patterned using resist, e.g., SiN or other hard maskmaterials. The mask 34 is removed in areas where SG devices (SG areas36) will be formed and remains in areas 38 where EG devices will beformed. This leaves areas 38 exposed. An ion implantation process isperformed to implant n-type dopants into the EG areas 38 to form highlydoped n-type regions 32 in the P well 22 and the N well 26.

Referring to FIG. 4, a nanosheet stack 40 is grown on the regions 32, Pwell 22 and N well 26. The stack 40 includes layers 44 and layers 46,which alternate. While other materials may be employed, it isadvantageous to grow the layers 44 of SiGe and the layers 46 of Siepitaxially to maintain crystal structure and lattice match theunderlying materials, e.g., Si. The SiGe layers 44 will then be removedlater in the process flow using, e.g., an HCl process, and the Si layers46 will remain to be used as the channel of the devices. A hard masklayer 42 is formed over the stack 40. The hard mask 42 may include asilicon nitride or other suitable materials.

Referring to FIG. 5, the hard mask 42 is patterned and employed to etchthe stack 40 to form nanosheet structures 50. The nanosheet structures50 are spaced apart from each other by a spacing pitch. A dummy gatematerial 52 is deposited over the top and in between the structures 50(going into the page). The dummy gate material 52 may include amorphousor polysilicon, although other materials may be employed. Additionally,there may be a dummy gate dielectric formed underneath the dummy gatematerial as well as a dielectric hard mask material on top of the dummygate material (not shown). The dummy gate material 52 is next patternedusing lithographic and dry etch processes. Spacers 45 are next formed bydepositing a conformal dielectric followed by employing a directionaldry etching process. After spacer formation source drain regions 47 arefabricated using CMOS process steps (e.g., epitaxial growth of dopedsemiconductor materials). An interlevel dielectric layer (ILD) 54 isthen deposited over the structures 50 and dummy gate 52. The ILD 54 mayinclude an oxide. A planarization process is employed to planarize thedielectric down to be coplanar with a top 56 of the dummy gates 52. Theplanarization process may include a chemical mechanical polishing (CMP)process.

Referring to FIG. 6, a process is performed to remove the dummy gatematerial 52 from over and in between the structures 50 (represented asexposed layers of the nanosheet structures in trenches 60). The dummygate open process may include a selective etch to remove dummy gatematerial (e.g., polysilicon) selectively to the materials of thestructures 50. The etch process removes a top portion of the ILD 54 andextends into the P well 22 and N well 26 for SG devices and through thedoped layer 32 and into the P well 22 and N well 26 for EG devices. Withthe removal of the dummy gate material 52 to open trenches 60, frontsand backs of the structures 50 are exposed in a dummy trench line withinthe ILD material 54.

Referring to FIG. 7, SG devices 62 are blocked by a mask 65. The mask 65is deposited and patterned to block the SG devices 62 and expose the EGdevices 64. The block or mask 65 may include a resist, a nitride, andoxide or other suitable material. Then, the ILD 54 protects portions ofthe EG devices 64 to provide a window over trenches 60. The etch processis directional and removes a sheets from the EG devices 64 in trenches60 down to a sheet 70. The removal of the sheets lowers a depth for thegate trench 60 and permits the formation of a thicker gate dielectriclayer. A remaining sheet 70, which remains in contact with layers 69 and71 (which may include an oxide or SiGe), will form a channel regionbetween the adjacent portions of the structure 50. Layers 69 and 71 willbe removed to release layer 70 in the next step. The mask 65 blockingthe SG devices 62 is then removed so that remaining SiGe layers (e.g.,not Si layers) for the SG regions 62 and the n-type doped regions 32 areremoved using, e.g., a dry HCl process. Etching occurs from exposed endportions of the regions to be removed. Alternating Si layers (75) remainfor the SG devices 62 with empty spaces (171) therebetween.

The present principles describe the structure 50 with threesemiconductor layers, where a single semiconductor layer is employed forthe EG devices 64. However, it should be understood that the number ofsemiconductor layers may be greater or less than the number shown andthat the EG devices 64 may employ more than one sheet for a channelregion.

Referring to FIG. 8, an etch is performed selective to Si layers toremove layer 69 to release layer 70. A bottom release region or area 72is formed where layer 32 was removed. Additional processing for forminggate dielectric layers for EG and SG devices is described beginning atFIG. 16.

Referring to FIG. 9, a perspective view of the device 10 is shown with agate structure 90 formed through structures 50. The gate structure 90shows spacers 92 and the single semiconductor layer 94 (or 70) releasedfor illustrative purposes. The gate structure 90 will include a gatedielectric layer, a gate conductor, barrier layers, etc. (not shown).The structures 50 include source and drain regions (47) with epitaxiallygrown portions 96. The gate structure 90 may include a cap 98.

Referring to FIG. 10, an alternate embodiment is shown where a top sheetis retained (instead of a bottom sheet), eliminating the need for thebottom release region as in FIG. 8. The process begins after the dummygate pull. A nanosheet stack 140 is grown on the substrate 12 with Pwells and N wells as described above. The stack 140 includes layers 144and layers 146, which alternate. While other materials may be employed,it is advantageous to grow the layers 144 of SiGe and the layers 146 ofSi epitaxially to maintain crystal structure and lattice match theunderlying materials, e.g., Si. The SiGe layers 144 may be converted tosilicon oxide or removed selectively with respect to the Si layers 146using an HCl etch at a later point in the process flow. A hard masklayer 142 is formed over the stack 140. The hard mask 142 may include asilicon nitride or other suitable materials. Trenches 130 are formedbetween the stack 140 and ILD 154.

Referring to FIG. 11, the trenches 130 are filled and the hard mask 142is covered by a dielectric material 148. The material 148 may be porousand include an oxide, an oxide glass, e.g., TEOS, etc. The material 148is planarized, e.g., using a CMP process. Then an etch process isperformed to open an EG device region 150 and form recesses 132.

Referring to FIG. 12, a spacer layer is conformally deposited to coverthe hard mask 142, the porous material 148 and exposed sidewalls of thestack 140 and the ILD 154. Sidewall spacers 160 are formed by adirectional etch to leave the spacers 160 on sidewalls. The spacermaterials may include a higher density oxide or nitride.

Referring to FIG. 13, the porous material 148 is removed from thetrenches 130 by an etch process. The topmost layer 146 is protected bythe hard mask 142 and sidewall spacers 160. The etch is selective to thematerials in the stack 140, the ILD 154 and the substrate 12.

Referring to FIG. 14, the layers 146 that are unprotected by the hardmask 142 and spacers 160 are removed by a selective etch process. Theetching process may etch a portion 138 of the substrate 12.

Referring to FIG. 15, the layers 144 are removed followed by the removalof the spacers 160. This leaves the topmost layer 146, which may beemployed as a device channel as described above for FIG. 1-9. FIGS.10-15 illustratively depict a process where the topmost layer 146 isemployed toe EG devices. The process steps and sequence follows themethods as described in FIGS. 1-9 even though certain details have beenleft out for simplicity.

Referring to FIG. 16, from the structure of FIG. 8, additionalprocessing is performed to form a gate structure 90 (FIG. 9), the blockmask 65 is removed. A first dielectric layer 170 is formed over the topof EG and SG devices and on the sidewall spacers 45 in the trenches 60.In one embodiment, the first dielectric layer 170 includes a conformaldielectric layer, e.g., oxide, which is deposited using, e.g., achemical vapor deposition process (CVD) or an atomic layer deposition(ALD) process. The deposited dielectric layer fills conformallyeverywhere including under the nanosheet structures 50 in release area72 and covers semiconductor layers/sheets 75 (e.g., Si) in the SGregions 62 and layer/sheet 70 in the EG regions 64. Empty spaces 171 aredisposed between layers/sheets 75 n the SG regions 62. An ALD process,in one example, is capable of depositing material under overhangswherever there is exposed surface to completely coat or fill thesurfaces of the release area 72, semiconductor layers/sheets 75 andlayer/sheet 70 with dielectric 170.

Referring to FIG. 17, the EG devices 64 are covered with a patternedblock mask 172. The first dielectric layer 170 is etched back on the SGdevices 62. An interface layer (IL) 174 is formed on the surface of theSG devices 62. The interface layer 174 may be formed using a chemicaloxidation process that selectively grows thin SiO₂ on the exposed SGsilicon regions 62. The block mask 172 can be removed before or afterthe chemical oxidation process.

Referring to FIG. 18, a high-k dielectric 176 is formed on both SGdevices 62 and EG devices 64. Processing continues with the formation ofadditional layers for forming a gate structure. Further processingincludes deposition of other materials to form the gate structures (FIG.19). After formation of the gate structure a planarizing step (e.g.,CMP) may be performed to remove layers from a top surface of the ILD 54.

Referring to FIG. 19, an example of a gate structure 180 is shown inaccordance with one illustrative embodiment. A cross-sectional view ofthe gate structure 180 is included between spacers 92 (45). The gatestructure 180 is formed on nanosheet 190. The nanosheet 190 includes aninterface layer (IL) 182, which is grown on or deposited on thenanosheet 190. The IL 182 may include an oxide or an oxynitride. Ahigh-k dielectric material 184 (176) is formed over the IL 182 and oversidewalls spacers 92. The high-k dielectric layer 184 and the IL 182form the gate dielectric for the gate structure 180. The nanosheet 190may include the bottommost sheet (e.g., sheet 70, FIG. 8) or the topmostsheet 146 (FIG. 15). For EG devices, the IL 182 may include a depositedoxide, or may include a grown oxide and a deposited oxide.

A diffusion barrier layer 186 may be formed on the high-k dielectriclayer 184. The diffusion barrier may include TiN, although othermaterials may be employed, such as, e.g., TaN, etc. A work functionsetting material 188 may be formed on the diffusion barrier layer 186. Amain conductor (not shown) may be formed on or within the work functionsetting material 188. The main conductor may include materials, such asW, Al, or other highly conductive materials. The gate length (L_(gate))is enlarged for EG devices by creating more room in the gate trench andby reducing pinch-off within the gate trench, which otherwise limitsgate dielectric thickness. The SG devices have a similar structure witha thinner dielectric that may include the high-k dielectric layer 184and a thinner IL 182, no ILD, a thinned deposited oxide or a grownoxide, etc.

Referring to FIG. 20, methods for forming semiconductor devices areprovided in accordance with the present principles. In some alternativeimplementations, the functions noted in the blocks may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

In block 202, a substrate is doped to form P wells for NFET devices andN wells for PFET devices to form a CMOS device. N wells and P wells formP-type and N-type devices for both SG devices and EG devices.

In block 204, a block or mask is formed on the substrate to cover singlegate (SG) regions. In block 206, a surface of the substrate in exposedareas where extra gate (EG) devices are to be formed is doped to form ahighly doped region at or near a surface of the substrate. This step andblock 204 are skipped if topmost semiconductor sheets are employed(e.g., blocks 240-252). In block 208, a stack (a nanosheet stack) ofalternating semiconductor and dielectric layers is formed on thesubstrate over single gate (SG) regions and the EG regions. Thenanosheet structures may include alternating layers of Si and SiGe orSiGe and silicon dioxide (the silicon dioxide layers may be removed). Ahard mask may be formed on the stack.

In block 210, the nanosheet structures may be formed by epitaxiallygrowing alternating layers of the Si and SiGe. In one embodiment, Ge maybe condensed (e.g., by annealing in the presence of oxygen) from theSiGe to turn the SiGe into oxide and the Si into SiGe. The stack ofalternating semiconductors (and/or dielectric layers) may include atleast three semiconductor layers. The some layers may be removed andreplaced later with semiconductor material for S/D regions.

In block 212, the stack is patterned to form nanosheet structures. Thenanosheet structures are longitudinally disposed and may be in the formof fin-like structures with multiple layers. In block 214, a dummy gatestructure is formed and patterned transversely over the fin-likenanosheet structures. In block 215, sidewall spacers are formed in adummy gate trench. In block 216, source and drain (S/D) regions areformed on opposite sides of the dummy gate structure. This may includeepitaxially growing S/D regions using the semiconductor layers at endpositions of the fin-like nanosheet structures. This process may beperformed at other times in the process sequence.

In block 217, an ILD layer is formed over the dummy gate structure. TheILD and dummy gate structure(s) are polished to expose the dummy gatestructure for a dummy gate pull. In block 218, the dummy gate structureis removed or pulled to form a trench in a dummy gate line over andbetween the nanosheet structures. In block 220, the SG regions areblocked to process the EG devices.

The method sequence splits depending on which of the semiconductornanosheets are to be employed to fabricate the EG device. One pathemploys the bottommost sheet or sheets while the other path employs thetopmost sheet or sheets.

In block 230, top sheets (semiconductor and dielectric layers) areremoved from the nanosheet structures along the dummy gate line. Inblock 232, at least one bottommost sheet is released to form a channelfor a field effect transistor device by etching away the highly dopedregion under the nanosheet structure and layers in contact with the atleast one bottommost sheet.

In an alternate path, in block 240, the hard mask is employed to patternthe stack to form nanosheet structures with gaps or trenches between theILD and the nanosheet structures. In block 242, a porous material (e.g.,a glass oxide or TEOS) is formed over the hard mask and over sides ofthe nanosheet structures. In block 244, the porous material is recessedin the trenches to a point below a topmost semiconductor layer of thenanosheet structures. In block 246, a spacer layer is formed over sideportions of the topmost semiconductor layer to protect the topmostsemiconductor layer. In block 248, the porous material is removed. Inblock 250, semiconductor layers of the nanosheet structures, which areunprotected by the spacer layer, are etched away for EG devices. Inblock 252, dielectric layers of the nanosheet structures for the EGdevices are etched away.

In block 254, a gate structure is formed in and over the dummy gatetrench wherein the remaining sheet or sheets of the semiconductor layerform a device channel for the EG device. By removing layers of thenanosheet stack more room is available for forming a gate dielectric forEG devices. The SG devices include thinner (e.g., 1-2 nm) gatedielectric than EG devices (e.g., 3-5 nm). The gate structure mayinclude forming an oxide on the remaining semiconductor sheet anddepositing a gate dielectric layer on the oxide. The processing mayalternate between EG devices and SG devices for forming the gatedielectrics. For example, EG devices and SG devices may be processedusing block masks to form gate dielectric layers, etching gatedielectric layers, etc. including different layers, different materials,different thicknesses, etc.

For example, in one embodiment, a first dielectric layer is depositedover the channel materials and one of the SG regions and the EG regionsis blocked by a block mask. A thickness of the first dielectric layer isthen adjusted by etching of adding additional material to the unblockedthe SG regions or the EG regions. The block mask is removed and the SGregions or the EG regions can then be processed together (e.g., a high-kdielectric or other layer may be deposited over both the SG regions andthe EG regions.

Then, a gate conductor is formed in the gate structure. Multiple layersmay be employed for the gate structure, e.g., oxide, high-k dielectriclayer, work function metal, main conductor, diffusion barriers, etc.

In block 258, processing continues to complete the EG and SG devices onthe CMOS device.

Having described preferred embodiments from an extra gate device fornanosheets (which are intended to be illustrative and not limiting), itis noted that modifications and variations can be made by personsskilled in the art in light of the above teachings. It is therefore tobe understood that changes may be made in the particular embodimentsdisclosed which are within the scope of the invention as outlined by theappended claims. Having thus described aspects of the invention, withthe details and particularity required by the patent laws, what isclaimed and desired protected by Letters Patent is set forth in theappended claims.

1. A semiconductor device, comprising: a substrate; nanosheetstructures, each including a stack of alternating layers on thesubstrate over single gate (SG) regions and extra gate (EG) regions, thenanosheet structures each including a central gate structure region andsource and drain regions on end portions of the nanosheet structures;and the central gate structure region including a single semiconductorlayer of the stack extending between the source and drain regions for EGdevices to enable a thicker gate dielectric for the EG devices.
 2. Thedevice as recited in claim 1, wherein the single semiconductor layerincludes a topmost semiconductor layer in the stack.
 3. The device asrecited in claim 1, wherein the SG regions form SG devices and the SGdevices include P-type and N-type devices.
 4. The device as recited inclaim 1, wherein the EG devices include P-type and N-type devices. 5.The device as recited in claim 1, wherein the central gate structureregion includes an interface layer as a gate dielectric, wherein theinterface layer further comprises an oxide and/or oxynitride.
 6. Thedevice as recited in claim 5, further comprising a high-k dielectricmaterial formed over the interface layer.
 7. The device as recited inclaim 6, further comprising a diffusion barrier layer formed on thehigh-k dielectric material.
 8. The device as recited in claim 7, furthercomprising a work function setting material formed on the diffusionbarrier layer.
 9. The device as recited in claim 8, further comprising amain conductor formed on the work function setting material.
 10. Thedevice as recited in claim 1, wherein the single semiconductor layerincludes a bottommost semiconductor layer in the stack.
 11. The deviceas recited in claim 10, further comprising a bottom release regionformed into the substrate below the bottom most semiconductor layer inthe stack and filled with a dielectric material.